This relates generally to imaging sensors, and more particularly, to imaging sensors with global shutter pixels that include LED flicker mitigation (LFM) structures.
In conventional imaging systems, image artifacts may be caused by moving objects, moving or shaking camera, flickering lighting, and objects with changing illumination in an image frame. Such artifacts may include, for example, missing parts of an object, edge color artifacts, and object distortion. Examples of objects with changing illumination include light-emitting diode (LED) traffic signs (which can flicker several hundred times per second) and LED brake lights or headlights of modern cars.
While electronic rolling shutter and global shutter modes produce images with different artifacts, the root cause for such artifacts is common for both modes of operation. Typically, image sensors acquire light asynchronously relative to the scenery being captured. This means that portions of an image frame may not be exposed for part of the frame duration. This is especially true for bright scenery when integration times are much shorter than the frame time used. Zones in an image frame that are not fully exposed to dynamic scenery may result in object distortion, ghosting effects, and color artifacts when the scenery includes moving or fast-changing objects. Similar effects may be observed when the camera is moving or shaking during image capture operations.
Conventional imaging systems also may have images with artifacts associated with low dynamic range. Scenes with bright and dark portions may produce artifacts in conventional image sensors, as portions of the image may be over exposed or under exposed.
It would therefore be desirable to be able to provide high dynamic range (HDR) global shutter imaging systems for capturing images with minimized artifacts related to moving objects, moving or shaking camera, flickering lighting, and objects with changing illumination.